Field-portable reflection and transmission microscopy based on lensless holography

Area of Science:

• Optics and Photonics
• Biomedical Engineering
• Microscopy

Background:

• Traditional microscopes can be bulky and expensive, limiting their use in field settings or resource-poor environments.
• Lensless microscopy offers a potential alternative, reducing size and cost.
• Holographic microscopy provides high-resolution imaging capabilities without complex optics.

Purpose of the Study:

• To develop a compact, portable, dual-mode holographic microscope capable of both transmission and reflection imaging.
• To achieve high resolution (≤2 µm) in a field-deployable format.
• To enable microscopic analysis in challenging or resource-limited settings.

Main Methods:

• Digital in-line holography for transmission mode, achieving unit fringe magnification for a wide field-of-view (FOV).
• Digital off-axis holography for reflection mode, using a beam-splitter to interfere reflected light with a tilted reference wave.
• Integration of both modes into a single, lightweight (~200 g) and compact assembly powered by batteries.

Main Results:

• Transmission mode achieved sub-pixel lateral resolution (≤2 µm) over a ~24 mm(2) FOV.
• Reflection mode, while having a reduced FOV (~9 mm(2)), also achieved sub-pixel resolution (≤2 µm) and is suitable for dense objects like tissue slides.
• The dual-mode microscope successfully imaged resolution targets, micro-particles, and a skin histopathology slide.

Conclusions:

• The developed lensless dual-mode holographic microscope is a cost-effective, portable solution for microscopy.
• Its dual imaging capability (transmission and reflection) broadens its applicability.
• This technology holds significant potential for field applications and microscopic analysis in resource-poor settings.